The present invention relates broadly to a digital phase shifter apparatus, and in particular to a low pass .pi. section digital phase shifter apparatus which is suitable for monolithic implementation.
In the prior art many electronic devices such as, for example, phased array systems utilize fundamental phase shifting circuits to achieve important functions. According to well-known prior art designs, phase shifters devices have generally required the use of circuits which employed a number of inductive elements. These prior art discrete element circuits are expensive since they must be built up element by element and to this date, it was not possible to implement an inductor into a monolithic or similar type circuit. In addition, the inductors which are rather expensive, add to the overall circuit cost.
Other prior art phase shifters have been developed to utilize digital techniques in obtaining the phase shift. However, the digital phase shifters in general are even more expensive than the discrete element inductive phase circuits, but they do have the distinct advantage of being mathematically predictable and are susceptible to monolithic implementation as well as batch processing.
At present, it is clear that none of the prior art phase shifters are able to satisfy the dual requirements of economy and small size. Therefore, it would be particularly desirable if such a circuit could be developed, particularly if such a circuit would be susceptible to a monolithic implementation capable such that it would be capable of being produced at low cost in large quantities.
Monolithic low-loss phase shifters at extra high frequencies (EHF) are highly demanded in the military market. In the previous works, two high pass T and .pi. sections and a low pass based T section digital phase shifters which are suitable for monolithic implementation were suggested. The operation of the new circuit is based upon the phase shifting characteristic of a low pass L-C, .pi. network. In the present invention, the complementary version of the low pass based T section is arranged in the form of a .pi. section digtal phase shifter to provide better insertion loss characterst1cs with improved phase tracking capability over the normal conventional approaches.